The specific aims of the Core for Protein Crystallization and X-ray Crystallography are to provide the necessary facilities and technical resources, including personnel, for the structure determination of the PGHS isozymes, bacterial cytochrome c oxidase and mutants thereof by X-ray diffraction techniques. The core will provide the following: 1. Preparation of purified protein samples for crystallization. This will include either assistance in or direct involvement in detergent exchange, in dialysis, and in the preparation of particular protein-ligand complexes for crystallization. 2- Design, development and setup of crystallization screens for the specific membrane proteins in the program project. This will include the screening of novel detergent systems for suitable crystallization conditions. 3. Characterization of crystals (e.g., SDS-PAGE, crystal density, etc.) including preliminary X-ray characterization, followed by any needed optimization for the crystallization protocols to grow X-ray quality crystals. 5. The X-ray Core personnel will design and execute X-ray data collection and data processing although, when appropriate, will also assist other members of the program project in data collection and processing. 6. The X-ray Core personnel will collaborate with members of the program project in the crystal structure analysis as well as provide any needed technical assistance and expertise for structure determination to individual members of the program project.